Re: [patch, fortran] PR66310 Problems with intrinsic repeat for large number of copies

[Jerry DeLisle <jvdelisle at charter dot net>]

On 07/12/2016 06:26 AM, Dominique d'Humières wrote:
>>> 2016-07-11  Jerry DeLisle  <jvdelisle@gcc.gnu.org>
>>>
>>> 	PR fortran/66310
>>> 	* simplify.c (gfc_simplify_repeat): Set max repeat to huge - 1 to allow
>>> 	one byte for null terminating the resulting string constant.
>>
>> OK, thanks
> Please hold on. I still see several problem with the patch applied. One is
> 
>    program p
>       character :: z = 'z'
>       print *, repeat(z, huge(1)-2**9)
>    end

Please test this revised patch. See my comments in the PR.

I think we should commit this one.

Jerry

diff --git a/gcc/fortran/gfortran.h b/gcc/fortran/gfortran.h
index 77831ab..dcacae8 100644
--- a/gcc/fortran/gfortran.h
+++ b/gcc/fortran/gfortran.h
@@ -59,6 +59,8 @@ not after.
 
 #define MAX_SUBRECORD_LENGTH 2147483639   /* 2**31-9 */
 
+/* Practical limit on size of character constants.  */
+#define MAX_CHAR_LENGTH 268435455    /* 2**28-1  */
 
 #define gfc_is_whitespace(c) ((c==' ') || (c=='\t'))
 
diff --git a/gcc/fortran/simplify.c b/gcc/fortran/simplify.c
index 8096a92..4010753 100644
--- a/gcc/fortran/simplify.c
+++ b/gcc/fortran/simplify.c
@@ -5085,24 +5085,29 @@ gfc_simplify_repeat (gfc_expr *e, gfc_expr *n)
   /* Check that NCOPIES isn't too large.  */
   if (len)
     {
-      mpz_t max, mlen;
+      mpz_t max, mlen, limit;
       int i;
 
-      /* Compute the maximum value allowed for NCOPIES: huge(cl) / len.  */
+      /* Compute the maximum value allowed for NCOPIES:
+	    huge(cl) - 1 / len.  */
       mpz_init (max);
       i = gfc_validate_kind (BT_INTEGER, gfc_charlen_int_kind, false);
 
+      /* Set the limit on size to avoid unsigned integer
+	 wrapping and resource limits.  */
+      mpz_init_set_si (limit, MAX_CHAR_LENGTH);
+
       if (have_length)
 	{
-	  mpz_tdiv_q (max, gfc_integer_kinds[i].huge,
-		      e->ts.u.cl->length->value.integer);
+	  mpz_tdiv_q (max, limit, e->ts.u.cl->length->value.integer);
 	}
       else
 	{
 	  mpz_init_set_si (mlen, len);
-	  mpz_tdiv_q (max, gfc_integer_kinds[i].huge, mlen);
+	  mpz_tdiv_q (max, limit, mlen);
 	  mpz_clear (mlen);
 	}
+      mpz_clear (limit);
 
       /* The check itself.  */
       if (mpz_cmp (ncopies, max) > 0)
diff --git a/gcc/testsuite/gfortran.dg/repeat_4.f90 b/gcc/testsuite/gfortran.dg/repeat_4.f90
index e5b5acc..a6ee75b 100644
--- a/gcc/testsuite/gfortran.dg/repeat_4.f90
+++ b/gcc/testsuite/gfortran.dg/repeat_4.f90
@@ -22,17 +22,17 @@ program test
 
   ! Check for too large NCOPIES argument and limit cases
   print *, repeat(t0, huge(0))
-  print *, repeat(t1, huge(0))
+  print *, repeat(t1, huge(0)) ! { dg-error "Argument NCOPIES of REPEAT intrinsic is too large " }
   print *, repeat(t2, huge(0)) ! { dg-error "Argument NCOPIES of REPEAT intrinsic is too large " }
   print *, repeat(s2, huge(0)) ! { dg-error "Argument NCOPIES of REPEAT intrinsic is too large " }
 
-  print *, repeat(t0, huge(0)/2)
-  print *, repeat(t1, huge(0)/2)
-  print *, repeat(t2, huge(0)/2)
+  print *, repeat(t0, huge(0)/8)
+  print *, repeat(t1, huge(0)/8)
+  print *, repeat(t2, huge(0)/16)
 
   print *, repeat(t0, huge(0)/2+1)
-  print *, repeat(t1, huge(0)/2+1)
-  print *, repeat(t2, huge(0)/2+1) ! { dg-error "Argument NCOPIES of REPEAT intrinsic is too large " }
-  print *, repeat(s2, huge(0)/2+1) ! { dg-error "Argument NCOPIES of REPEAT intrinsic is too large " }
+  print *, repeat(t1, huge(0)/8+1) ! { dg-error "Argument NCOPIES of REPEAT intrinsic is too large " }
+  print *, repeat(t2, huge(0)/16+1)! { dg-error "Argument NCOPIES of REPEAT intrinsic is too large " }
+  print *, repeat(s2, huge(0)/16+1)! { dg-error "Argument NCOPIES of REPEAT intrinsic is too large " }
 
 end program test